Three-electrode semiconductor device



Patented Sept. 2, 1952 THREE-ELECTRODE SENHCODUCTOR DEVICE John P. Stelmak, Forest Hills, N. Y., assigner to Radio Corporation of America, a corporation n oi' Delaware Appli'ationMay 3 1, 1949, serial No. 96,956

This invention relates generally to semiconf ductor devices vand particularly `to a novel con.-`

struction for a. three-electrode semi-conductor amplifier, oscillator or thelike.

The three-electrode semi-conductor is a recent development in the field of electronic amplifica--` tion. This device is presently knownas a tranf sister, and its essential characteristics have beendisclosed in a series of three letters to .the Physical Review by Bardeen and Brattain, Brattain and Bardeen, and Shockley and Pearson which appear on pages 230 to 2.33` ofthe July l5, 1948y issue. The new amplifier device includes a block of a semi-conducting material such as siliconor germanium which is provided with two closely adjacentpoint electrodes called emitter and collector electrodes in contact with one surface region of the material, and a base electrode which provides a large-area, low-resistance contact with another surface region of the semi-conductor. The input circuit of the am,- pliiier described in the publicationreferred to above is connected between the emitter electrode and the base electrode while the output circuit is connected between the collector electrode and the base electrode. In this circuit the base `electrode is the common input and output electrode and may, therefore, be grounded.

A semi-conductor device of the type described in the publications referred to is rather difcult to manufacture. The semi-conducting material is provided withv two point electrodes consisting of wires which are spaced apart approximately two mils. Thus, it will readily be seen that the exact positioning of the point electrodes is fairly diflicult. Furthermore, the pressure between the two point electrodes and the semi-conductingmaterial should lbe fairly high inorder to provide the required contact between the electrodes and 'the semi-conducting material. :Since theA wires from which the point electrodes are made have a diameter of the'order of 5 mils or less, they mustbe made of a stiff spring-like metal in order to obtain the required contact pressure.,` However, since a germanium crystal is very hard and brittle,l the contactv betweenthe crystal and a stii, hard metal such as. tungsten is relatively poor. It is believed that this causes a considerable noiseYdueoto-:minute variations of the conf 'tact areas between the electrodesand the crystal.

Another drawback of the conventional semiconductor device as described in the publications referred to and elsewhere is the small heat dissipation-of thepoint electrodes due to their small, mass. Furthermore, the power output which can be obtained with a conventional three-electrode semi-conductor am'pliiier'is limited. This is also believed to be due' at least in part togthe small contact areas between the point electrodes and the Lcrystaland also due to the small diameters of the electrodes. t v k,It is accordingly the principal object ofthe present invention to' provide an improved multif electrode semi-conductorV device suitablehfor use as an' amplienoscillator or the like purposes whichis easier to manufacture, has a better me; chanical stabilityv and improved' electrical 'charf' acteristies. I Y l 'A further object of the invention is to provide a novel three-electrode semi-conductor device which permits a higher contact pressure between the semi-conducting crystal and itsVsmall-area electrodes thereby to decrease the noise caused by variations of the contact pressure between the electrodes and the crystal. f

Another object of the invention is to provide a semi-conductor device of the type referred to having a higher heat dissipation and permitting larger power outputs than previously known semi-conductor devices having point electrodes. In accordancer with the present invention a block or cube of semi-conducting material is provided having a substantially straight edge. The two small-area lelectrodes of the device may consist of conductive or metallic ribbons or strips arranged parallel to each other and at right angles to the edge of the semi-conducting mate rial. The metallic ribbons may be provided with knife edges for contacting the edge ofthe semif conducting n. material thereby to decrease the, point-like contact areas betweenr the ribbons `and the semi-conducting material. construction permits the use ofa softer metal such as Pinosphor bronze for theelectrodes which can better. follow the irregular microscopic surfaceof vthe crystal, therebyto provide a better contact bea-3; tween the electrodes and the semi-conducting material. Furthermore, ahigher contactv pressure mayl be obtained which also tends to reduce` noise caused by variation of the contact pressure;

y Finally, the heat dissipation as Well vas the power.

output of the device of the invention are very.

good. y i, The /novel features that are considered char.-

' acteristic of this invention are set forthwith par.:`

ticularity in the appended claimsn'lhek invention itself, however, `both as to its organization;

and method of operation,as well as additional objects and'advantages thereof, will best be un': derstood Yfrom the following description when read in connection with the accompanying draw-.z ing, in which:

components have been designated by the samek reference numerals throughout vthe `iig-uros, andi particularly to Figures l to 3, there is illustrated 7 a semi-conductor device embodying the present invention which may be used aegon,-v 'amplifien oscillator or the like. The device comprises a block or cube I D of semi-conducting Amaterial consisting, for example, of a semi-conducting element such as germanium, silicon, boron, tel-` y a suitable opening 1n the lower portion of the lurium or selenium containing a small but suicientnumber of. atomicdipurity centersor lattice imperfections as"l commonly employed for best results insemiiconducltor devicesisuch as crystal rectiers. Germanum Ythe preferred material for block l0 and 'may be prepared so asA 'tofbe an electronic N typej semi-conductor as is well known. The surface of yserni-conducting block lgmay Vbe 'polished and etched in themanner explained vingt'lie paper byfBardeen and Brattain referred'fto. vItis' also feasible to 'utilize the. gerfianium' "bloclrl from af'fc'ornrnerciall 'highebackvoltage germanium rectifier" ""such' as j type 1 N34 in which case further surface j treatrnentV may notbetreunred; j j

As clearlyjshown in :Figure '1, blbck I 'may 'have the shape of `a. cube or 'semi-'conducting material. However, all4 that is necessary that "the 'upper portion Aof block- Ill v'is ofv wedged' shape to provide a substantially straight Vedge II 4on which the small-area electrodesrmaybear; Thns,'block I0 may be providedwiththreeor'more electrodes, that is, withk 'a large-area low-impedance 'base electrode and withtwo lsmall-area .electrodes whichmay be'used as the` emitter and collector electrodes in -a threeeelectrorle semi-conductor amplifier.` Block I"0 lis-electrically connected Aand securedtome'tallie 'stud'V I2r `whicl-i may, for example, consistof brass. StudA I j-is provided-with a suitable wedge-shaped aperture I3V for receiving `the loWerpo-r-tion ofblock I-to-whieh it may be soldered.A Stud --I2-' -preferably has la circular cross section as Vclearly shown inv FigureZ.

' The two -sxnall-area-eleotrodes consist-of two metallic ribbonsforstrips45,16; Ribbons I5, 'Hi may, for/example, consist of a -small'stripfof a high tensile strengt bronze sheet material wloi'c-hY may for example, have a thickness of 5 mils.; -Asclea y? Figures 11 andf; ribbons 1 5, 'IGi-areleach' provided with aknifeetlgeforratgclriseli*point Il; I Shaving" a fine edge ofiappronirnately .5 milf thickness;

showin controlled-"inpho direction, `tha supports 22, 23 from rotating with respect to cylinder 25. Cylinder 25 is provided with a suitable bore 28 which may have a. square cross section with rounded corners as illustrated in Figure 2. Stud I2 has a press t with cylinder 25 and may be forced upwards to engage block I0 with metal- 11C Vribbns I5, y s- .i i' j As clearly shown in theLidraW-ing', kr'iife,'edges II, I8 extend substantially at right angles with straight edge II of block I0. Accordingly, the contact area between metallic ribbons I5, I6

-which represent Ythe emitter and collector elec- -trodes and block I0 is very small or point-like.

,'Ihe distance between knife edges I1 and I8 may Q .be of the order .of 2 mils.

The semi-,conductor device of the invention is assembled in the following manner. At rst,

- .block 'I 0* is soldered or sweated tostud I2 which may `then be provided with a wire 30 received in stud to facilitate electrical connection to stud. ,I2 which .functions 'asgthe ibase electrode. Now; supports 212 and'23'areinserted cylinder A Ziiancl ribbonsr I5', VH5 'arepwelded orjotherwise" secured' to their respective'rsupports. Ca-re should betaken that k'rufe'Y edges'II, 4LIlifare substantially Yparallel to each other; that their spacing'correspondsto a predeterminedv *va-lue andjtlfrat 'tlieyare both lo'cated-in a coinrnon plaire.v1 lIt willi-be obvious' thatposi-tionf'Qk-nife-'edges I-'l, neetlfonly be A only'-v the spacing*V betweeirthel -linife1 -edges' "must `conform tothe desired-"vaine;E New, 'stud li2isf pushed- 'or forced-through; peni-ngilfuntil edge II` of block I' *contacts both nieta "-iibbons 115' and: TE. Finally. studi' lf2 *is -pushedlafurther'predetermined distancel Vinto- Acylinder 25 Vto provide thefrequired contact pressure between knife edges Il," I8 and' breakin. i f

Ribbons I5, Iii' 'should' :consist-of a 'suitablel metal which 'ifsncomparative'lysofit to insure an intimate eontactnbetween-knifefedges -I'lf'I, 'I-B and? the microscopic irregularities ofthestraight'ledge Il of block lf3'. Furthermore; the materialfof' whichl ribbons 155,1?6' consist should be sulciently stii` to provide theoesired contact pressurei It will be* evident that the horizontal portions of ribbons I5, -Il-wlill-bend when 'block IIl-is pus-hed upwards against' the'- ribbons; thereby toprovide' the required pressure.- --Due tothe :99' degrees twistV vin ribbons I5, Illth'evcross-s'ectionof the? ribbons atltheir welds-lpresent a large momen-t' Thechiselpointsmay, for-example, form-an angletozfacilitatetheir connection to 'supports'.Y 22 and 23 to which they may be welded or other-3 wiselifasteneda. .Supports;22,23may consist-ofl a suitable metallic wiresuch,l as nickel. s: Y

.Y SnpportsZZ. and 235 are Afperrnanently secured tnzandfextemi througln cylinder :2'5 consisting of a.

suitable insulatingmaterial Asuolo as Bakelite. .As shown the Adrawirng;'supports 22:, 2.3 are: .prot

vided with. locking flats-261,11 .extending through4 suitablexsluts lcylinder 25. Illisiwill prevent of inertia.' Normally, a Phosphor bronzewire `orstripl becomes-"rather: sort' -adacentthe vweld andl consequently4 bendsl at4 thislfpoint. Since ribbons I5, IIB are:arrangedlvertically adjacent their l three-electrode 'semil-eond-uctor" device 'sui-'table' as fan 'amplienhoscillatore# fthe Alike vpurposes'.- The small-area :electrodes of the device;that-"1is, the emitter andcolleotorelectrodes are -ofl very;I

rugged :constructionwhich-:permits lnghejr`4 con" i tact pressures than liavev` been obtained-heretofore. Furthermore, the particular desif'gfnof the small-area electrodes' Y-tl'ieforiny ofilatnie'tallio ribbons will 'prbvid-afbetter 'spring v'acticin' so ea; refer: ,el eine i Home meer may be utilized. This, in turn, will provide a more intimate contact between the electrodes and the semi-conducting material which considerably reduces noise due to variations of the contact pressure. Furthermore, the heat capacity of the small-area electrodes is larger which in turn improves the heat dissipation and permits higher output power. The device of the present invention is mechanically superior to previously known semi-conductor devices and its electrical characteristics are equal to or superior to previously known semi-conductor devices having point electrodes.

What is claimed is:

l. A semi-conductor device comprising a cubeshape block of semi-conducting material having a substantially straight edge, a first electrode providing a low-resistance contact with said block, a second and a third electrode, each consisting of a ribbon of high tensile strength and softer than said block, each of said ribbons having a bend and a substantially right angle twist intermediate its ends, a metallic support for one end of each of said ribbons, the other end of each of said ribbons being provided with a knife edge, said supports being disposed with respect to said block so that said knife edges are disposed substantially at right angles with respect to said straight edge, and means for pressing the knife edges of said ribbons against said straight edge to provide intimate contacts of relatively small areas between said ribbons and said block.

2. A semi-conductor device comprising a block of semi-conducting material having substantially a straight edge, a conductive member having an opening shaped to receive said block. said member providing a relatively low-resistance contact with said block, a pair of additional conductive supports extending in a plane intersecting said straight edge, two conductive ribbons, each being provided with a bend and a substantially right angle twist intermediate its ends and having one end secured to one of said pair of supports, the free ends of said ribbons being provided with knife edges, said ribbons being secured to said supports so that their knife edges are disposed substantially parallel to each other and at right angles to said straight edge of the block, and means for pressing said ribbons against said straight edge to provide a relatively small intimate contact between each of said ribbons and said block.

3. A semi-conductor device comprising a cube of semi-conducting material having a substantially straight edge, a metallic stud having a Wedge shape opening for receiving said cube and for providing a large-area Contact with said cube, a pair of metallic supports extending vertically on opposite sides of said straight edge, two metallic ribbons, each being provided with a rightangle bend intermediate its ends and with a right angle twist and having one end secured to one of said supports, the free ends of said ribbons being provided with knife edges, said ribbons being disposed with their knife edges substantially parallel to each other and at right angles to said straight edge, and means for pressing said ribbons against said straight edge to provide a relaltively small intimate contact between each of said ribbons and said cube.

JOHN P. STELMAK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,410,268 Carlson Oct. 29, 1946 2,486,776 Barney Nov. 1, 1949 2,502,479 Pearson et al Apr. 4, 1950 FOREIGN PATENTS Number Country Date 21,408 Great Britain Apr. 9, 1908 599,341 Great Britain Mar. 10, 1948 

